An oil coalescing filter is a device performing coalescence of oil, or a device used to collect oil. Oil coalescing filters are primarily used to separate emulsions into their components via various processes. A coalescer can be divided into mechanical and electrostatic coalescers. Mechanical coalescers use filters or baffles to make droplets coalesce while electrostatic coalescers use DC or AC electric fields (or combinations). The instant invention is directed toward a mechanical coalescer, also known as a coalescing filter. One common use of a coalescing filter is in an industrial sized compressor and/or vacuum, like a rotary screw compressor/vacuum package or a liquid ring compressor/vacuum package.
In the area of compressed air purification, coalescing filters are used to separate liquid water and oil from compressed air using a coalescing effect. These oil coalescing filters may additionally remove particles. Coalescing filters can be used for many purposes in the compressed air field, like in industrial size refrigeration units. As other examples, in the Natural Gas industry, gas/liquid coalescers are used for recovery of lube oil downstream of a compressor, and in the Oil and Gas, Petrochemical and Oil Refining industries, Liquid-Gas coalescers are widely used to remove water and hydrocarbon liquids from natural gas to ensure natural gas quality and protect downstream equipment.
In industrial sized compressors and or vacuums, like a rotary screw compressor/vacuum or a liquid ring compressor/vacuum, the coalescing filter is utilized for removing liquids from the air stream. Liquids from upstream of the compressor, which may include aerosol particles, entrained liquids or large volumes of liquids called “slugs” and which may be water and/or a combination of hydrocarbon liquids are removed by a filter/coalescing vessel located upstream of the compressor. Thus, the coalescing filter provides a means for filtering or cleaning the resulting air stream. However, lube oil recovery is the primary reason for installing a coalescer on the outlet of a compressor/vacuum.
A rotary screw compressor/vacuum package or a liquid ring compressor/vacuum package includes an electric or gas motor to turn a compressor, an oil separator tank/oil sump, air intake filter, oil filter, various piping for moving the compressed air/gas, electrical and pneumatic controls for controlling and monitoring the compressor, and an air or water cooled oil cooler/radiator for cooling the air and oil. Depending on the size of the compressor/vacuum, these units require large volumes of expensive compressor oil for operation. It is vital to the operation of the compressor that the oil separator system is designed to keep oil loss at a minimum.
Along with the air or gas to be compressed, large amounts of compressor oil are injected into the compression chamber. This oil aids in compression, lubricates, and acts as a coolant. After exiting the compression chamber, the hot air-gas/oil mixture flows through a pipe into the separator tank (oil sump) where the oil is removed from the air-gas stream. As the oil laden air/gas mixture flows through the pipe and into the separator tank, large amounts of liquid oil will fall down into the oil sump due to the velocity being reduced to a minimum as it enters the larger vessel. Smaller particles of oil remain mixed in the air-gas stream in the form of light mist. If not removed and allowed to remain in the air-gas stream, this oil mist can quickly deplete the compressor oil to dangerous levels and can damage the compressor/vacuum or environment.
An oil coalescing filter, like the one of the instant invention, is housed within the separator tank, also known as the oil sump. The primary function of the separator element is to trap as much of the remaining oil mist as possible before the air-gas is discharged from the compressor package. To date, the efficiency of the best designs will yield approximately 3-5 parts per million by weight. Depending on the end use requirement, the remaining oil leaving the compressor package is either allowed to proceed downstream to the end user or separated and filtered further using finer filtration stations along the piping system. Consequently, it is highly desired that the coalescing filter remove as much oil and contaminant from the air/gas leaving the compressor package.
While the oil coalescing filter, i.e. the separator element, traps and collects the oil mist, the element must also maintain a low pressure differential, or back pressure on the compressed air or gas. Compressor/vacuum packages are typically recommended to have a pressure differential, or pressure loss, to be in the range of 2-3 pounds per square inch (psi) across newly installed separator elements. High differential pressure results in high power consumption and potential high oil carryover. As such, compressor/vacuum manufactures typically recommend that the oil coalescing filter be changed when pressure differential reaches approximately 10% of the system pressure. As a result, it is also highly desired that the coalescing filter provide as low of pressure differential as possible to increase the efficiency of the package and to extend the life of the filter.
A typical separator filter element is constructed with two stage filtration. The first stage typically consists of a bed of fine fibers to coalesce the oil mist into large droplets. The large droplets are then collected and transported within a bed of larger fibers to a point where the oil will pool up then the liquid will be picked up and recirculated through the compressor package. This final pick up process is referred to as an oil scavenging return system.
The life of the coalescing filter, or separator element, depends on how much contaminate reaches the filter. Contaminate will plug up the fine pores of the larger fiber bed building back pressure until the element reaches the point that change out is required. One problem with current designs of coalescing filters and the filter media used therein, is that it retains all of the oil trapped in the filter and provides no way of releasing the oil once trapped. This results in loss of compressor oil in the system, a build up of pressure differential over time of use in the coalescing filter, and frequent change outs of the coalescing filter. Consequently, it is preferred to provide a coalescing filter that is able to release the oil once trapped to prevent loss of compressor oil in the system, to reduce the build up of pressure differential over time of use in the coalescing filter, and to reduce the change outs of the coalescing filter.
Another problem associated with coalescing filters is static electricity. Oil is conductive and is a carrier of atoms. Thus, the more oil left in the air/gas stream and the more oil stored in the coalescing filter, the more risk of static electricity effecting the package. This can obviously become a dangerous situation and is thus sought to be reduced and/or eliminated.
The instant invention is designed to provide an oil coalescing filter that addresses the problems mentioned above.